The present invention relates generally to a length or angle measuring arrangement and more particularly to a length or angle measuring arrangement which includes a graduation carrier including a measuring graduation and reference mark fields.
Devices for generating photoelectric electrical signals in length or angle measuring arrangements are known in the art. For example, a position measuring arrangement of this type is disclosed in German DE-C2-3416864. This reference discusses the problems which are peculiar to the generation of reference impulses in such position measuring arrangements and suggest possible solutions to such problems. In the disclosed device, the arrangement of the photodetectors is governed by the wavelength of the light as well as by the orientation of the grid parameters of the phase grids.
However in such arrangements the measuring result may be impaired for example through refracted partial beam bundles of higher order which impinge or fall upon detectors that are allocated or dedicated to other partial beam bundles which are of lower order. Further, if there are geometric and/or optical changes in the measuring arrangement, errors can occur if the individual allocations described above are deviated from further.
Therefore, in view of the above, it is a primary object of the present invention to provide a scanning arrangement wherein a reference mark is scanned in a high-resolution position measuring arrangement having a very large scanning space in relation to the resolution of the measuring graduation of the arrangement.
It is a further object of the present invention to provide a measuring arrangement which is insensitive to tilting, turning, scanning-distance changes, aging of the light source, and other interfering factors to thereby provide a clear allocation of the reference marks to the scanning graduation which remain constantly preserved.